Paper Citing NAMD - Abstract
Rui, Xianliang; Mehrbod, Mehrdad; Van Agthoven, Johannes F.; Anand, Saurabh; Xiong, Jian-Ping; Mofrad, Mohammad R. K.; Arnaout, M. Amin
The alpha-Subunit Regulates Stability of the Metal Ion at the Ligand-associated Metal Ion-binding Site in beta(3) Integrins
JOURNAL OF BIOLOGICAL CHEMISTRY, 289:23256-23263, AUG 15 2014
The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin beta A domain of the beta-subunit through a divalent cation at the metal ion-dependent adhesion site (MIDAS). An auxiliary metal ion at a ligand-associated metal ion-binding site (LIMBS) stabilizes the metal ion at MIDAS. LIMBS contacts distinct residues in the alpha-subunits of the two beta 3 integrins alpha(IIb)beta(3) and alpha(V)beta(3), but a potential role of this interaction on stability of the metal ion at LIMBS in beta(3) integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated beta 3 integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded alpha(IIb)beta(3) versus alpha(V)beta(3), the result of stronger interactions of LIMBS with alpha(V), which reduce stability of the LIMBS metal ion in alpha(V)beta(3). Replacing the alpha(IIb)-LIMBS interface residue Phe(191) in alpha(IIb) (equivalent to Trp179 in alpha(V)) with Trp strengthened this interface and destabilized the metal ion at LIMBS in alpha(IIb)beta(3); a Trp179 to Phe mutation in alpha(V) produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular alpha(IIb)beta 3 and a W179/F substitution in alpha(V)beta(3) reduced and increased, respectively, the apparent affinity of Mn2+ to the integrin. These findings offer an explanation for the variable occupancy of the metal ion at LIMBS in alpha(V)beta(3) structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation.
